Poured concrete may be reinforced by a grid of metal rods. The metal rods are often referred to as “Rebar”, which is short for reinforcing bar, and are often made of coated steel. The grid is formed by placing a lower layer of rods approximately perpendicular to an upper layer of rods, thus forming a “crisscross” or “checkerboard” pattern of metal rods with space between the individual rods. At the intersections where the upper and lower rods touch, a twisted wire is often used to mechanically bind the upper and lower rods together. Additionally, after wrapping and twist tightening, each wire generally must be cut so it does not extend to the surface of the concrete after pouring. The twisted wires also are generally flattened after cutting so that if someone were to fall on the rebar grid before the concrete is poured, they would not be skewered by the otherwise protruding wire ties. Whether the wires are wrapped around the upper and lower rods, twist tightened, cut, etc. by hand or with a wire tying machine, significant labor is required. There is also a potential hazard arising from omission of the wire flattening step.
U.S. Pat. No. 4,110,951 describes a prior attempt at elimination of the wire tying process involving the forcing of a clip over the perpendicular intersection of the upper and lower rods. The clip includes a passage for the upper bar and an independent passage for the lower bar, but relies on deformation of the clip in the two planes of the rebar grid to hold the clip in place after the clip is forced over the perpendicular rods. As the clip lacks a way to hold the bars together if a vertical or downward force is applied to the lower bar, the lower bar can separate from the clip if forced downward, such as by a worker walking on the lower bar. While it is possible to arrange the bars in an interleaved manner where a first longitudinal bar is lower and an adjacent second longitudinal bar upper, separation of the lower bar from the clip can still occur if the spacing between adjacent bars in the same plane is wide enough. Having to maintain close spacing of adjacent bars and properly alternating every adjacent bar between the upper and lower positions may increase material cost over what is necessary to adequately reinforce the concrete and significantly increases the labor and skill required to assemble the grid before the concrete is poured.
As can be seen from the above description, there is an ongoing need for simple and efficient materials and methods for forming rebar grids prior to pouring concrete over the grid. The devices of present invention overcome at least one of the disadvantages associated with conventional devices for rebar attachment.